It is make your mind up time. This week, the Intergovernmental Panel on Climate Change, set up by the UN in 1988, will publish a paper that will form a crucial part of its fifth assessment report. It will reaffirm that climate change is happening, is manmade and that the balance of evidence is that it is accelerating dangerously. It is the work of 259 scientists from 39 countries who have to submit their work to detailed and open scrutiny before the panel will publish. It is global science's best assessment – hedged with probabilities and acknowledging uncertainties – of where we are. We should be desperately concerned.

However, it will be met by a barrage of criticism from the new "sceptical" environmental movement – almost entirely on the political right – which, while conceding that global temperatures are rising, insists that there is still insufficient scientific proof to make alarmist predictions. There is certainly no need for governments to tax and regulate the burning of fossil fuels, or subsidise renewables, or come to "freedom-denying" international agreements. Economic growth, technology and the magic of human adaptation through tried and tested market mechanisms will see civilisation through what is already an over-hyped crisis.

Don't be bamboozled, as Britain's centre-right media move to join with the sceptics to rubbish a careful body of scientific work that has been arrived at by exhaustive cross-examination. We will be reminded of the IPCC's earlier "mistakes", notably its estimate in the 90s that global average temperatures were rising by 0.15C a decade, when since then they have risen at a third of that rate.

We will be told it is beating a retreat. Any slip will be seized on as proof positive of the IPCC's effort to dupe the global public. Doubtless, as a UN initiative, there will be efforts to characterise it as the product of Marxists and deluded socialists. BBC attempts to broadcast its findings in as impartial way as possible will be portrayed as yet more evidence of BBC bias, even though the BBC will pack its coverage with lots of sceptical voices, notwithstanding their marginalisation by world science, to try to cover its back. By the week's end, the risk is you will be less certain than you are now, tempted to join the apparent new consensus that there is no need for an urgent response. The sceptics will have done their job and national – let alone international – action will be more remote.

The IPCC is keenly aware that its findings will be mercilessly challenged. In the documents seen by the Observer, it sticks to unassailable facts. Global average surface temperatures have risen by 0.89C since 1901 and 0.6C since 1950. It is 95% likely that the cause is human activity, notably burning fossil fuels and deforestation.

A further increase in temperatures is certain: what is uncertain is by how much. It could be as little as 0.3C by 2100, the lowest boundary of one of four scenarios. Or it could be as high as 4.5C, the upper boundary of the highest scenario. Threading its way through the probabilities, the IPCC's best guess is that temperatures by the end of the century will be at least two degrees higher than pre-industrial levels, with a much greater risk they could be higher than lower.

This is terrifying. The decades ahead will witness our planet become progressively uninhabitable for hundreds of millions of people, because of either drought or floods. The weather will become ever more volatile. Ocean currents will be disturbed and dwindle. There will be mass movements of people trying to escape the consequences; no country will be untouched. We should act to minimise the risk.

Yet the highly ideological rightwing mind does not think in this way. Any call for collective action is to be instinctively distrusted, along with those who make it. Their motives must be suspect and the evidence on which they make their appeal necessarily flawed. The world did not make progress through government and public action, however it may appear. Rather, it is a matter of faith that it advanced only through self-help and individual enterprise, guided by the invisible hand of the market. Climate change that challenges this faith system is necessarily a gigantic scam, backdoor socialism.

Thus the slowdown in the growth of global temperatures over the past decade obviously reveals the scam. The alternative hypothesis – that the world's oceans have been absorbing the heat in ways we do not yet understand – is ignored. The bigger project is to discredit "climate change socialism".

Science has not helped its own cause. The open science movement, and even the Royal Society, has become concerned that the quest to win commercial funding has made a growing number of scientists too anxious to make their science unique. Too many scientific papers are published in which researchers make it hard for others to reproduce their lab experiments. Key data are omitted.

Compared with what is happening in some drug and cancer research, climate change science is remarkably honest, reproducible and subject to open criticism: the IPCC insists on the best methodology. But for climate change sceptics such as Andrew Montford, Bjørn Lomborg or Nigel Lawson's influential Global Warming Policy Foundation, this is an inconvenient truth. Climate change science must be greeted with the same sense that science in general is fallible.

This helps their case, but so does the widespread resignation that politics and government are inefficient and helpless, a view propagated by the right on a daily basis. For example, in the 1930s and 40s, Britain reacted to homelessness by building towns to house our growing population. No such optimism or belief in public purpose exists today. Over the past 20 years, 2.8m new households have formed. Only 130,000 new social housing units have been built. If we can't build homes, what chance is there of arresting global warming?

On top of all this, there is the astonishing political economy of Britain's media. The duty of newspapers to impart information as objectively and truthfully as possible, keeping comment rigorously separate, has been progressively dropped. After all, in a post-Enlightenment, postmodern universe, there are no objective truths, only points of view. Right-of-centre newspapers are now edited ruthlessly to make their readers think what their editors and proprietors want – on immigration, welfare, Europe, tax, political affiliation or whatever. Climate change has joined the list.

It is a lethal cocktail. Yet truths will out. Public and private are interdependent spheres: capitalism rests on public as well as private initiative. There are scientific truths. There is, however imperfectly, a "we". Politics and government can and do make a difference. The rise in global temperatures, and its consequences, is happening. This is a battle of ideas as much as for our civilisation. It is a battle that has to be won.